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Algae Identified as Cause of Rare Infections

March 24, 2015

Algae Identified as Cause of Rare Infections

There are thousands of microbes relevant to clinical microbiology, each with their own appearance in culture, but conventional wisdom is that none of them are green. It was therefore surprising when two green organisms were recovered in pure culture from otherwise-healthy patients who suffered injuries in fresh water in geographically distant Missouri and Texas during the summer. Both patients initially seemed well, but after presentation to the hospital soon suffered signs of infection: swelling and redness of the injured knee and foot, respectively, associated with fever and leukocytosis. In both cases, abundant green colonies were recovered in fungal culture of sterile surgically-obtained specimens. No pathogens were recovered in various other cultures, implicating this organism as the cause of the infections. Genetic analysis identified both isolates as belonging to the same species of algae, Desmodesmus armatus.

Algae are ubiquitous in nature in both natural and manmade aquatic habitats. Algae of the genus Prototheca are well known as a rare cause of disease in humans and animals but are notable for their lack of chlorophyll in spite of their classification as "green algae". Their lack of chlorophyll makes them dependent on other sources of energy and has, historically, been hypothesized to be related to their tendency to infect mammals. Still, true green algae have also been demonstrated, often at autopsy or necropsy, to cause human and animal infection. Their green color is noted in fresh samples but disappears with fixation, resulting in organisms that look like achlorophyllic Prototheca in pathological sections. Because Prototheca were once thought to be decendents of a chlorophyllic alga named Chlorella, the type of infectious disease caused by a green algae was named "chlorellosis" in the absence of a firm identity for the causative microorganism.

Our case report identifies two cases of "chlorellosis" from geographically distant sites and establishes the infectious agent as the algae Desmodesmus armatus. This is the first report to definitively establish the etiologic agent of this rare disease. The successful surgical approach to patient management reported here, the culture conditions used to isolate the organisms, the genetic approach to identification, and the potential to treat chlorellosis with antifungals as protothecosis sometimes is will allow others to better diagnose and manage infections due to chlorophyllic algae.

These two cases were reported in the March 5th New England Journal of Medicine with Dr. Bradley Ford as corresponding author.

L. F. Westblade, S. Ranganath, W. M. Dunne, C.-A. D. Burnham, R. Fader, and B. A. Ford, "Infection with a Chlorophyllic Eukaryote after a Traumatic Freshwater Injury, "New England Journal of Medicine, vol. 372, no. 10, pp. 982–984, Mar. 2015.